ELPHINSTONE, MARGARET MERCER, Comtesse de Flahault, Viscountess Keith, and Baroness Nairne (1788–1867), only child of George Keith Elphinstone, viscount Keith [q.v.], admiral, by his first wife, Jane, only child and heiress of William Mercer of Aldie, Perth, was born in Hertford Street, Mayfair, 12 June 1788, and in 1789 lost her mother, to whose right to the barony of Nairne (at that time in attainder) she then succeeded. She was early brought into the circle of the Princess Charlotte of Wales, whose attached friend and confidante she became; and this position raised a rumour against her (which, however, she was able entirely to refute) that she betrayed the princess's secrets to the prince regent. On 20 June 1817, at Edinburgh, she married the Comte de Flahault, aide-de-camp to Bonaparte, who had been educated in this country, and had taken refuge here on the restoration of the Bourbons. The countess took a prominent place in society. Her husband held office under the Bourbons. He was ambassador successively at Rome, at Vienna, and (1860) at St. James's, and finally resided at Paris as chancellor of the Legion of Honour. The countess took part in all his social and political work. References to her hospitalities abound in Moore's letters and diary and elsewhere.

The countess died at her husband's official residence, Paris, on 13 Nov. 1867, aged 79. She had two children, daughters, the elder of whom (who succeeded to her English and Irish titles) was Downger Marchioness of Lansdowne at the time of her death, and the younger. Mlle, de Flahault, was unmarried. [Allardyce's Memoirs of G. K. Elphinstone, 58, 418-19; Gent. Mag. lxxxvii. ii. 81; Times, 15 Nov. 1867, p. 7, col. 2; Russell's Moore, iii. 98, 99, 104, 111, 112, &c., vii. 186, &c.; see also Miss Knight's Autobiography.]